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PubMed1997

Spatial orientation in humans: perception of angular whole-body displacements in two-dimensional trajectories.

Vestibular perception of whole-body passive rotation in the horizontal plane was studied by applying two-dimensional (2D) motion to eight blindfolded healthy volunteers: pure rotations in place, corner-like trajectories and arcs of a circular trajectory were randomly applied by means of a remotely controlled robot. Angles embedded in the 2D trajectories were 45 degrees, 90 degrees, 135 degrees and 180 degrees. Stimulation of semicircular canals was the same for all trajectories but was accompanied by concurrent otolith stimulation during circular motion. Subjects participated in two successive experimental sessions. In the first session they were instructed to use a pointer to reproduce the total angular displacement after the motion (REPRODUCTION); in the second session they had to keep pointing towards a remote (15 m) memorised target during the motion (TRACKING). In REPRODUCTION subjects tended to overestimate their rotation angle by 28 +/- 11% (mean +/- SD). There was no systematic effect of the trajectory. Overestimation also occurred when subjects were required to rotate in darkness by 180 degrees (by controlling a joystick). In TRACKING there was virtually no overestimation (6 +/- 17%) and the movement of the pointer matched the dynamics of angular motion. We conclude that (a) the brain can separate and memorise the angular component of complex 2D motion; however, a large inter-individual variability in estimating its amplitude exists; (b) in the range of linear accelerations used in the study, no appreciable effect of otolith-canal perceptual interaction was shown; (c) angular displacements can be dynamically transformed into matched pointing movements; (d) overestimation seems to be typical of delayed judgements of angular displacement and of self-controlled rotations in place. This could be due to the characteristics of the physiological calibration of the vestibular input.

Humans↗
PubMed2001

Curved saccade trajectories: voluntary and reflexive saccades curve away from irrelevant distractors.

In this study we examined the impact of irrelevant distractors upon trajectories of reflexive and voluntary saccades. Observers made saccades to visual targets above and below fixation as directed by target appearance (reflexive) or by a central directional cue (voluntary) in the presence of an irrelevant distractor stimulus (a cross) whose appearance was simultaneous with target onset. We recorded saccade latency, amplitude and the magnitude of saccade curvature relative to the direct route from the start-to-end of the saccade. Previous studies of saccades curvature have used distractors to provide information about the saccade task and, as a result, have only examined trajectories of voluntary saccades. However, we have shown that both reflexive and voluntary saccades curved away from irrelevant distractors. The effect of irrelevant distractors indicates that observers do not need to attend to distractors in a voluntary fashion for distractors to modify saccade trajectories. Furthermore, it highlights an important parallel in curvature of saccades and reach trajectories, namely that both curve away from irrelevant distractors. The second important observation was that reflexive, as well as voluntary, saccades curved away from distractors. This suggests that curvature is not solely a consequence of voluntary control. These results have been considered within the context of inhibition-based theories of curvature derived from studies of saccade and manual reach trajectories.

Adolescent↗
PubMed2004

A model of the saccade-generating system that accounts for trajectory variations produced by competing visual stimuli.

Variable saccade trajectories are produced in visual search paradigms in which multiple potential target stimuli are present. These variable trajectories provide a rich source of information that may lead to a deeper understanding of the basic control mechanisms of the saccadic system. We have used published behavioral observations and neural recordings in the superior colliculus (SC), gathered in monkeys performing visual search paradigms, to guide the construction of a new distributed model of the saccadic system. The new model can account for many of the variations in saccade trajectory produced by the appearance of multiple visual stimuli in a search paradigm. The model uses distributed feedback about current eye motion from the brainstem to the SC to reduce activity there at physiologically realistic rates during saccades. The long-range lateral inhibitory connections between SC cells used in previous models have been eliminated to match recent physiological evidence. The model features interactions between visually activated multiple populations of cells in the SC and distributed and topologically organized inhibitory input to the SC from the SNr to produce some of the types of variable saccadic trajectories, including slightly curved and averaging saccades, observed in visual search tasks. The distributed perisaccadic disinhibition of SC from the substantia nigra (SNr) is assumed to have broad spatial tuning. In order to produce the strongly curved saccades occasionally recorded in visual search, the existence of a parallel input to the saccadic burst generators in addition to that provided by the distributed input from the SC is required. The spatiotemporal form of this additional parallel input is computed based on the assumption that the input from the model SC is realistic. In accordance with other recent models, it is assumed that the parallel input comes from the cerebellum, but our model predicts that the parallel input is delayed during highly curved saccadic trajectories.

Animals↗
PubMed2006

Examining Ambrosia pollen episodes at Poznań (Poland) using back-trajectory analysis.

The pollen grains of Ambrosia spp. are considered to be important aeroallergens in parts of southern and central Europe. Back-trajectories have been analysed with the aim of finding the likely sources of Ambrosia pollen grains that arrived at Poznań (Poland). Temporal variations in Ambrosia pollen at Poznań from 1995-2005 were examined in order to identify Ambrosia pollen episodes suitable for further investigation using back-trajectory analysis. The trajectories were calculated using the transport model within the Lagrangian air pollution model, ACDEP (Atmospheric Chemistry and Deposition). Analysis identified two separate populations in Ambrosia pollen episodes, those that peaked in the early morning between 4 a.m. and 8 a.m., and those that peaked in the afternoon between 2 p.m. and 6 p.m.. Six Ambrosia pollen episodes between 2001 and 2005 were examined using back-trajectory analysis. The results showed that Ambrosia pollen episodes that peaked in the early morning usually arrived at Poznań from a southerly direction after passing over southern Poland, the Czech Republic, Slovakia and Hungary, whereas air masses that brought Ambrosia pollen to Poznań during the afternoon arrived from a more easterly direction and predominantly stayed within the borders of Poland. Back-trajectory analysis has shown that there is a possibility that long-range transport brings Ambrosia pollen to Poznań from southern Poland, the Czech Republic, Slovakia and Hungary. There is also a likelihood that Ambrosia is present in Poland, as shown by the arrival of pollen during the afternoon that originated primarily from within the country.

Air↗
PubMed2006

Substance use disorder trajectory classes: diachronic integration of onset age, severity, and course.

BACKGROUND: Substance use disorders (SUDs) may be characterized by onset age, severity, substance type, course, and outcomes. SUD phenotypes in the literature typically consider each of these features in isolation. Conceptual frameworks and data collection procedures for assessing SUD phenotypes are increasingly "diachronic" in approach, providing for characterizations "throughout time". The recent availability of statistical procedures for the identification of latent classes offers the possibility of developing SUD phenotypes integrating these developmental features. This article illustrates the utilization of SAS-TRAJ mixture modeling to characterize variations in SUD symptom trajectories to define phenotypes. METHODS: The subjects were 332 adult males with SUDs. Their course of symptoms from early adolescence through middle adulthood was retrospectively determined. Symptom trajectories were defined by the number of DSM-IV SUD symptoms by year of age. SAS-TRAJ mixture models identified trajectory classes. Model development, evaluation, and selection using this approach are discussed. RESULTS: Among these men with SUDs, six trajectory classes were identified, including groups characterized by early-onset and severe SUD symptoms persisting into adulthood, an early-onset group similar in adolescence but improving in adulthood, and other groups with symptoms emerging later with varying degrees of severity and persistence. The SUD trajectory classes were significantly different on comorbid psychopathology, particularly childhood disruptive behavior disorders. CONCLUSION: The results present a new method for the comprehensive depiction of heterogeneity in SUD symptoms. Future studies may determine the extent to which SUDs phenotypes based on the course of symptom development inform etiology, prevention and treatment research.

Adolescent↗
PubMed2003

Trajectories of delinquent behaviour in adolescence and their covariates: relations with initial and time-averaged factors.

This longitudinal study examined individual, family, and peer covariates of distinctive trajectories of juvenile delinquency, using data from a community sample of 318 German adolescents (mean age at the first wave was 11.45 years). Latent growth mixture modelling analysis revealed four trajectory groups: high-level offenders, medium-level offenders, low-level offenders, and rare offenders. The trajectory groups were discriminated better by time-averaged covariates than by initial status covariates. High peer tolerance of deviance and low parental empathy were consistently linked to varying offending trajectories, whereas gender, low academic achievement, and low parental monitoring appeared to be trajectory-specific covariates.

Adolescent↗
PubMed2023

Phenotypic presentation of Mendelian disease across the diagnostic trajectory in electronic health records.

PURPOSE: To investigate the phenotypic presentation of Mendelian disease across the diagnostic trajectory in the electronic health record (EHR). METHODS: We applied a conceptual model to delineate the diagnostic trajectory of Mendelian disease to the EHRs of patients affected by 1 of 9 Mendelian diseases. We assessed data availability and phenotype ascertainment across the diagnostic trajectory using phenotype risk scores and validated our findings via chart review of patients with hereditary connective tissue disorders. RESULTS: We identified 896 individuals with genetically confirmed diagnoses, 216 (24%) of whom had fully ascertained diagnostic trajectories. Phenotype risk scores increased following clinical suspicion and diagnosis (P < 1&#xa0;&#xd7; 10-4, Wilcoxon rank sum test). We found that of all International Classification of Disease-based phenotypes in the EHR, 66% were recorded after clinical suspicion, and manual chart review yielded consistent results. CONCLUSION: Using a novel conceptual model to study the diagnostic trajectory of genetic disease in the EHR, we demonstrated that phenotype ascertainment is, in large part, driven by the clinical examinations and studies prompted by clinical suspicion of a genetic disease, a process we term diagnostic convergence. Algorithms designed to detect undiagnosed genetic disease should consider censoring EHR data at the first date of clinical suspicion to avoid data leakage.

Humans↗
PubMed2005

Particle deposition onto micropatterned charge heterogeneous substrates: trajectory analysis.

A trajectory analysis of particles near a micropatterned charged substrate under radial impinging jet flow conditions is presented to investigate the effect of surface charge heterogeneity on particle trajectory and deposition efficiency. The surface charge heterogeneity is modeled as concentric bands of specified width and pitch having positive and negative surface potentials. The flow distribution is obtained using finite element analysis of the governing Navier-Stokes equations. The particle trajectory analysis takes into consideration the hydrodynamic interactions, gravity, van der Waals and electrostatic double layer interactions. The presence of surface charge heterogeneity on the substrate gives rise to an oscillating particle trajectory near the collector surface due to repulsive and attractive forces. As a result of the coupled effects of hydrodynamic and colloidal forces, the particle trajectories and deposition efficiencies are increasingly affected by surface charge heterogeneity as one moves radially away from the stagnation point. The results indicate that it is possible to render collectors with up to 50% favorable surface fraction completely unfavorable by modifying the ratio of the radial to normal fluid velocity. Utilizing the real favorable area fraction of the collector, the patch model expression for calculating the deposition efficiency is modified for impinging jet flow geometry.

Journal Article↗
PubMed2005

Travel time and trajectory moments of conservative solutes in two-dimensional convergent flows.

We address advective transport of a solute traveling toward a single pumping well in a two-dimensional randomly heterogeneous aquifer. The two random variables of interest are the trajectory followed by an individual particle from the injection point to the well location and the particle travel time under steady-state conditions. Our main objective is to derive the predictors of trajectory and travel time and the associated uncertainty, in terms of their first two statistical moments (mean and variance). We consider a solute that undergoes mass transfer between a mobile and an immobile zone. Based on Lawrence et al. [Lawrence, A.E., Sánchez-Vila, X., Rubin, Y., 2002. Conditional moments of the breakthrough curves of kinetically sorbing solute in heterogeneous porous media using multirate mass transfer models for sorption and desorption. Water Resour. Res. 38 (11), 1248, doi:10.1029/2001WR001006.], travel time moments can be written in terms of those of a conservative solute times a deterministic quantity. Moreover, the moments of solute particles trajectory do not depend on mass transfer processes. The resulting mean and variance of travel time and trajectory for a conservative species can be written as functions of the first, second moments and cross-moments of trajectory and velocity components. The equations are developed from a consistent second order expansion in sigmaY (standard deviation of the natural logarithm of hydraulic conductivity). Our solution can be completely integrated with the moment equations of groundwater flow of Guadagnini and Neuman [Guadagnini, A., Neuman, S.P., 1999a. Nonlocal and localized analyses of conditional mean steady state flow in bounded, randomly non uniform domains 1. Theory and computational approach. Water Resour. Res. 35(10), 2999-3018.,Guadagnini, A., Neuman, S.P., 1999b. Nonlocal and localized analyses of conditional mean steady state flow in bounded, randomly non uniform domains 2. Computational examples. Water Resour. Res. 35(10), 3019-3039.], it is free of distributional assumptions regarding the log conductivity field, and formally includes conditioning. We present analytical expressions for the unconditional case by making use of the results of Riva et al. [Riva, M., Guadagnini, A., Neuman, S.P., Franzetti, S., 2001. Radial flow in a bounded randomly heterogeneous aquifer. Transport in Porous Media 45, 139-193.]. The quality of the solution is supported by numerical Monte Carlo simulations. Potential uses of this work include the determination of aquifer reclamation time by means of a single pumping well, and the demarcation of the region potentially affected by the presence of a contaminant in the proximity of a well, whenever the aquifer is very thin and Dupuit-Forchheimer assumption holds.

Kinetics↗
PubMed2005

A Cxcl12-CXCR4 chemokine signaling pathway defines the initial trajectory of mammalian motor axons.

Motor neurons, alone among neurons in the vertebrate CNS, extend axons out of the neural tube to innervate peripheral targets. Two classes of motor neurons, termed vMNs and dMNs, extend axons out of the neural tube via ventral and dorsal exit points, respectively, in accord with their homeodomain transcription factor repertoire. Downstream of these transcriptional codes, the cell surface receptors that shape initial motor axon trajectories have not been identified. We show here that the chemokine receptor Cxcr4 is expressed on the axons of vMNs as they follow their ventral trajectory, whereas its ligand, Cxcl12, is expressed by mesenchymal cells surrounding the ventral neural tube. Genetic studies reveal that Cxcl12-Cxcr4 signaling directs the ventral trajectory of spinal vMNs. In its absence, these neurons adopt a dMN-like trajectory, despite preservation of their vMN transcriptional identity. Thus, the status of Cxcr4 signaling helps to determine the initial axonal trajectory of mammalian motor neurons.

Animals↗
PubMed2006

Particulate sulphate and nitrate in Southern England and Northern Ireland during 2002/3 and its formation in a photochemical trajectory model.

Daily measurements of sulphate and nitrate are reported from Harwell in southern England and Belfast in Northern Ireland for the period 2002/3. When the higher percentiles are compared with the mean concentration, nitrate reveals considerably greater episodicity than either sulphate or PM(10) (measured by TEOM). A photochemical trajectory model using the Master Chemical Mechanism scheme has been used to predict daily concentrations of both nitrate and sulphate aerosol over the period March to August 2002 at the Belfast and Harwell sites. This has been carried out for daily samples using 72, 96 and 120 h air mass back trajectories obtained from both the British Atmospheric Data Centre and the HYSPLIT on-line service. Additionally, model simulations have been conducted for 5 trajectories generated through clustering of the trajectories for individual days. This reveals an under-prediction of the model associated particularly with trajectories originating from the European mainland. In general, the model performs reasonably well in simulating concentrations of both nitrate and sulphate, which is surprising given that the model does not account for processes requiring the presence of liquid water. This suggests that aqueous phase oxidation processes may not make a major contribution to airborne sulphate concentrations in the U.K. in the spring and summer months. It appears that inclusion of explicit ammonium nitrate formation chemistry may be essential to reliable prediction of episodic nitrate peaks.

Aerosols↗
PubMed2003

On-line trajectory modifications of planar, goal-directed arm movements.

Sometimes a goal-directed arm movement has to be modified en route due to an unforeseen perturbation such as a target displacement or a hand displacement by an external force. In this paper several aspects of that modification process are addressed. Subjects had to perform a point-to-point movement task on a computer screen using a mouse-coupled pointer as the representation of the hand position. Trajectory modifications were imposed by unexpectedly changing the position of the target or by changing the relation between mouse and screen pointer. In the first series of experiments, we examined how often a trajectory is updated. Here, trajectory modifications were imposed by unexpectedly changing the normal relation between mouse and pointer to a shear-like relation, where a percentage of the forward/backward position of the hand was added to the pointer position in the left/right direction. Withdrawal of visual feedback during the movement revealed that trajectories were updated at interval times shorter than 200 ms. From the similarity with experiments where the original relation between mouse and pointer was restored during the movements, we conclude that motor plans are updated on-line to move the hand from its current perceived position to the target. In a second series of experiments, we studied whether a continuous change in target position yields similar trajectory modifications as a continuous hand displacement. To mimic the latter perturbation, we used the above-mentioned distortion of the mouse-pointer relation. We found that the resulting hand paths did not differ for the two visual perturbations and conclude that the perturbed, goal-directed movements are modified in a consistent way, irrespective of whether the position of the target or hand was perturbed. Simulations of the experimental data with a kinematic reaching model support this conclusion.

Acceleration↗
PubMed1999

Effects of kinematics constraints on hand trajectory during whole-body lifting tasks.

Trajectories of the hands and whole-body center of mass were studied during whole-body lifting tasks. The movements of different parts of the body were monitored with the ELITE system. Subjects were instructed to lift to shoulder height an object placed at one of two distances (5-45 cm) before them on the floor. The lifts were performed both with and without kinematics constraints (i.e. to produce a straight hand trajectory while lifting, and to lift without any instructions, respectively). Hand trajectories were roughly straight when performed under the constrained condition, but curved when performed without instruction. Hand velocity curves showed bell-shaped profiles. In both groups, body centers of mass (whole-body, upper and lower part) were calculated and their trajectories showed invariant sagittal displacements. These results support the idea that movement contributes to postural control and, reciprocally, that whole-body center of mass is a robust and controlled variable which plays an important role in hand trajectory formation.

Adult↗
PubMed2001

Correspondence analysis of sinogram lines. Sinogram trajectories in factor space replace raw images in the orientation of projections of macromolecular assemblies.

The lines of a large group of sinograms of projections with random orientation can be submitted to correspondence analysis. Since the number of samples per line is small, a small matrix is accumulated which is quick to orthogonalise. In the eigenvector space, the lines of a sinogram are represented by points describing a closed trajectory. Two trajectories of different sinograms intersect in the position of their common line. Determining where two trajectories cross each other is a problem of minimum chi2 distance in the space of 5-7 eigenvectors. An algorithm to determine common lines has been implemented and tested with phantom projections oriented at random, and corrupted with noise. The images were simulating a set collected with the two exposures technique, already proposed by the authors for three dimensional reconstruction from random projections. The preliminary models obtained with the new algorithm have been refined by a projection matching based on trajectories. This step requires determining which trajectory, in a set representing computed projections, matches at best with that of an experimental projection. This is a problem of minimum distance in a space with low dimensionality. The present algorithms, based on chi2 distances, run much faster than those based on correlation analysis and the quality of the reconstructed phantoms looks satisfactory.

Journal Article↗
PubMed2002

A trajectory-based algorithm to determine and refine Euler angles of projections in three-dimensional microscopy. Improvements and tests.

An improvement of the trajectory matching algorithm is presented, which is based on the use of the derivative of trajectories and of the projection of experimental sinogram lines in the factor space determined by sinogram lines of projections of a model. The algorithm performance is illustrated by use of different phantom structures, to show the effect of symmetry on trajectory matching. A GroEL complex has also been reconstructed from both cryo-negatively stained and unstained frozen-hydrated samples. The refinement of this structure has been carried out by the trajectory matching algorithm as well as by conventional cross-correlation methods. Slight differences among the two results are discussed. The improved trajectory matching algorithm, based on chi2 distances, runs much faster than correlation analysis and looks satisfactory as for the quality of the reconstructed structures.

Journal Article↗
PubMed2002

Developmental trajectories of cigarette use from early adolescence into young adulthood.

This study identified developmental trajectories of cigarette smoking from early adolescence into young adulthood, and delineated whether risk factors derived from a social learning-problem behavior framework could differentiate among trajectories. Participants (N=374) were interviewed five times from age 12 until age 30/31. Using growth mixture modeling, three trajectory groups were identified--heavy/regular, occasional/maturing out, and non/experimental smokers. Being a female, having higher disinhibition, receiving lower grades, and more frequent use of alcohol or drugs significantly increased the probability of belonging to a smoking trajectory group compared with being a nonsmoker. Higher disinhibition and receiving lower grades also differentiated regular smokers from the rest of the sample. None of the risk factors distinguished occasional from regular smokers. When models were tested separately by sex, disinhibition, other drug use, and school grades were associated with smoking for both sexes. On the other hand, environmental factors, including socioeconomic status, parent smoking and friend smoking, were related to smoking for females but not for males. Sex differences in developmental trajectories and in smoking behavior among regular smokers were notable. Future research should examine transitions and turning points from adolescence to adulthood that may affect cessation and escalation differently for males and females.

Adolescent↗
PubMed2003

Examining trajectories of adolescent risk factors as predictors of subsequent high-risk driving behavior.

PURPOSE: To examine the effects on early high-risk driving behavior of changes over time (trajectories) in adolescent alcohol use, friends' support for drinking, susceptibility to peer pressure, and tolerance of deviance. METHODS: Statewide driving data were obtained for 4813 subjects who had completed at least two previous school-based questionnaires. The self-administered questionnaire data provided predictor measures from 5th through 10th grades. Trajectory information on predictor measures was summarized using each measure's slope over time and level at the 10th grade data collection (last value). Regression models used serious offenses, alcohol-related offenses, serious crashes, and alcohol-related crashes as outcomes, trajectory measures as predictors, and produced parameter estimates adjusted for demographic measures. Probabilities of having a serious offense or serious crash for five sample trajectories on each measure were obtained from the estimated regression models. RESULTS: All four predictor measures were important, particularly in predicting serious offenses, alcohol-related offenses, and alcohol-related crashes. The highest probabilities for young adult high-risk driving were found among those with consistently high or increasingly high trajectories of friends' support for drinking, susceptibility to peer pressure, and tolerance of deviance. CONCLUSIONS: Programs to prevent adolescent risk behavior should take into account environmental and personality influences. Prevention efforts need to emphasize preserving low levels, preventing increases, and promoting decreases over time of adolescent risk factors for unhealthy behaviors, such as high-risk driving.

Accidents, Traffic↗
PubMed2003

Developmental trajectories of boys' delinquent group membership and facilitation of violent behaviors during adolescence.

Being part of a delinquent group has been shown to facilitate the expression of an individual's own delinquent propensities. However, this facilitation effect has not been investigated from a developmental perspective within a population heterogeneity model. Using a semiparametric mixture model with data from the Montreal Longitudinal Experimental Study, this article addresses important issues in the developmental trends of membership to delinquent groups. We explore how the rate of violent behaviors follows delinquent peer group trajectories and investigate a differential facilitation effect of delinquent peers on violence across multiple developmental pathways. Results suggest that 25% of males followed a childhood or an adolescence delinquent group affiliation trajectory. These two groups account far most of the violent acts assessed during adolescence. In addition, the rate of violent behaviors follows these developmental trajectories. Controlling for these delinquent group trajectories, we also found that being involved in a delinquent group at any specific time during adolescence is associated with an increased rate of violent behaviors, and that leaving these groups results in a decrease in violent behaviors. This facilitation effect appears homogeneous over time and across developmental trajectories. Results are discussed from a social interactional perspective.

Adolescent↗